An illustration of a brain with advanced Alzheimer's. / Stacy Jannis/Alzheimer's Association

by Karen Weintraub, Special for USA TODAY

by Karen Weintraub, Special for USA TODAY

Alzheimer's disease accounts for many more deaths than we've realized, a new study concludes, making it nearly as lethal as the nation's two biggest killers, heart disease and cancer.

Death certificates record immediate cause of death, but often miss the underlying cause, which is why Alzheimer's has been undercounted, according to Bryan James, an epidemiologist at Rush University Medical Center in Chicago, who led the research.

The new study, published today in the journal Neurology, found that annual death rates from Alzheimer's should be closer to 500,000 than the 85,000 currently counted by the government. Heart disease and cancer both account for more than 500,000 deaths per year.

James and his colleagues followed more than 2,500 older adults who had agreed to donate their brains to research upon death. The autopsies that accompanied that donation allowed researchers to definitively determine whether they had Alzheimer's, and to calculate from that the percentage of Americans who die with the disease.

"There's no doubt that Alzheimer's is underreported" as a cause of death, said James Leverenz, an Alzheimer's expert and director of the Center for Brain Health at the Cleveland Clinic in Ohio. He was not involved in the new study.

"Having Alzheimer's listed as only 5% of individuals who are dying is a disservice to the disease," he said. "Knowing more about precisely how big a contributor it is helps us make better health policy."

Alzheimer's rates are also expected to skyrocket as Baby Boomers reach their 70s and 80s, when Alzheimer's is most common. Roughly half of people over 85 have some kind of dementia, other figures show.

"We need to come to grips with how we're going to manage this in the future," Leverenz said.

Research last year also suggested that Alzheimer's is nearly as lethal as heart disease and cancer, and that it may be costlier than the other two, said Kenneth Langa, an epidemiologist and professor at the University of Michigan who helped conduct that research. Both cancer and heart disease receive far more federal research funding for basic research, however, he said.

Alzheimer's is always lethal, but because most people think of it as a memory disease, they do not always connect the disease with death, said James, the new study's author. He estimates that dementia cuts five to 10 years off the lifespan and is not a normal part of aging.

"If you develop Alzheimer's, you are going to die a lot earlier than someone who does not," James said.

The confusion of dementia can lead to lethal falls that would not have happened otherwise. Pneumonia is also common among with people with Alzheimer's, whose bodies have literally forgotten how to shift the throat muscles to keep food from the lungs.

Sometimes, the cause of death is listed as something other than Alzheimer's because a diagnosis of Alzheimer's was never made or because of a combination of denial, ageism and stigma, said Meryl Comer, CEO and president of the Geoffrey Beene Foundation Alzheimer's Initiative, and a board member of the advocacy group USAgainstAlzheimer's.

"If you look at many of the obituaries, they rarely say Alzheimer's, it's usually pneumonia - for many of us, that's the unspoken line that says they probably had Alzheimer's," said Comer, a former television personality who has spent more than 18 years caring for her husband who has early-onset Alzheimer's. "No one wants to be remembered that way."

Leading causes of death in the U.S. in 2010

(A new study suggests that Alzheimer's actually kills approximately 500,000 people per year, and so should fall third on this list instead of sixth)